(1) Field of the Invention
This invention relates to methods of forming small contact holes using triple exposure of either a positive radiation sensitive layer or a negative radiation sensitive layer.
(2) Description of the Related Art
U.S. Pat. No. 5,863,712 to Von Bunau et al. describes a method of forming a projected image or photosensitive dielectric pattern that is faithful to a designed pattern without performing complex correction of a mask pattern.
U.S. Pat. No. 5,958,656 to Nakao describes a pattern forming method using a first exposure using a first phase shift mask and a second exposure using a second phase shift mask.
U.S. Pat. No. 5,455,144 to Okamoto et al. describes an exposure technology for a semiconductor integrated circuit device which has a pattern as fine as that of an exposure wavelength.
U.S. Pat. No. 6,022,644 to Lin et al. describes a mask containing a subresolution line to minimize proximity effect of a contact hole.
U.S. Pat. No. 5,308,741 to Kemp describes a lithographic method using double exposures, physical mask shifting, and light phase shifting to form masking features on a substrate masking layer.
U.S. Pat. No. 6,238,850 B1 to Bula et al. describes a method of forming an image having reduced corner rounding in a photosensitive dielectric layer.
U.S. Pat. No. 5,702,868 to Kellam et al. describes a method of fabricating a plurality of high resolution images in a radiation sensitive material.
U.S. Pat. No. 6,184,151 B1 to Adair et al. describes a method of forming square shape images in a lithographic process.
U.S. Pat. No. 5,422,205 to Inoue et al. describes a method of transferring a micropatttern onto a substrate. The method comprises forming a multilayer film consisting of at least two layers on the substrate. The uppermost layer is exposed using a first mask. The layers other than the uppermost layer are exposed using a second mask.